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ATEL # 982; K-band Spectroscopy of AX J1841.0-0536 and IGR J19140+0951
on 30 Jan 2007; 10:14 UT
Password Certification: Juan Fabregat (email@example.com)
Subjects: Infra-Red, Binaries, Neutron Stars
Referred to by ATEL #: 983
Spectroscopy in the K band of the AX J1841.0-0536 and IGR J19140+0951 optical/infrared counterparts was obtained on 2006 July 14, using the SofI spectrograph/imager attached to the ESO 3.5m NTT in La Silla, Chile (ESO proposal 077.D-0578(A)). The spectra cover the 2.02-2.28 Ám range with a dispersion of 4.62 ┼/pixel and S/N~150. Observations were carried out in poor weather conditions, under a partially clouded sky.
AX J1841.0-0536 (IGR J18410-0535): We observed 2MASS 18410043-0535465, the optical/infrared counterpart identified by Halpern et al. (2004, ATel #289). The main lines in the spectrum are HeI (2.0581Ám) in emission, and HeI (2.1126Ám) and Br-gamma in absorption. In addition, NIII/CIII (2.1155Ám) is present in emission, and CIV (2.069 and 2.078Ám) in weak emission. These signatures are characteristic of a mid to late O type supergiant. However, the very weak or absent HeII (2.1885Ám) line together with HeI (2.0581Ám) seen in emission indicate a spectral type not earlier than O9-B0. The estimated spectral type is B0I, with an uncertainty of two subtypes. This classification confirms the nature of AX J1841.0-0536 as a Supergiant Fast X-ray Transient (SFXT), as proposed by several authors from its X-ray emission behavior (e.g. Negueruela et al. 2005, ESA-SP 604, 165).
IGR J19140+0951: We observed 2MASS J19140422+0952577, the infrared counterpart identified by in 't Zand et al. (2006, A&A 448, 1101). The spectrum is dominated by HeI (2.0581Ám) in emission, and HeI (2.1126Ám) and Br-gamma in absorption. NIII/CIII (2.1155Ám) is also present as a weak emission line, while HeII (2.1885Ám) is absent. The spectral type is estimated at B1I. IGR J19140+0951 is a Supergiant X-ray Binary (SGXB).